Warm-up method and warm-up system for internal combustion engine

ABSTRACT

A warm-up system is provided for an internal combustion engine equipped with a CO 2  absorbing and releasing agent that absorbs CO 2  at a temperature in a first temperature range and releases the CO 2  at a temperature in a second temperature range that is higher than the first temperature range. The warm-up system increases a temperature of the CO 2  absorbing and releasing agent to reach the second temperature range such that the CO 2  released from the CO 2  absorbing and releasing agent is supplied to a component of the internal combustion engine such as an intake manifold and an exhaust gas purification catalyst.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a warm-up method and a warm-up system for aninternal combustion engine equipped with a CO₂ absorbing and releasingagent.

2. Description of Related Art

A CO₂ absorbing and releasing agent that absorbs CO₂ in a temperaturerange approximately at 500° C., and releases the absorbed CO₂ in atemperature range higher than the aforementioned temperature range hasbeen well known as disclosed in publication titled TOSHIBA REVIEW (vol.56, no. 8 (2001) pp. 11-14). The similar technology is also disclosed inJP-A-11-262631.

The CO₂ absorbing and releasing agent that has been heated to reach asubstantially high temperature range equal to or higher than 500° C.releases CO₂ at high temperature. It has not been considered to use suchhigh temperature CO₂ for warm-up of the internal combustion engine.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a warm-up method and awarm-up system for an internal combustion engine for promoting thewarm-up of the internal combustion engine using CO₂ released from theCO₂ absorbing and releasing agent.

A warm-up method for an internal combustion engine is provided with aCO₂ absorbing and releasing agent so as to be able to absorb CO₂contained in an exhaust gas in a first temperature range, and to releasethe CO₂ absorbed therein in a second temperature range that is higherthan the first temperature range. In the warm-up method, a temperatureof the CO₂ absorbing and releasing agent is increased to be brought intothe second temperature range so as to supply the CO₂ released from theCO₂ absorbing and releasing agent into a component of the internalcombustion engine.

In the above-described warm-up method for the internal combustionengine, the high temperature CO₂ released from the CO₂ absorbing andreleasing agent may be supplied to the components of the internalcombustion engine so as to be quickly warmed up.

In the warm-up method, an exhaust gas purification catalyst thatpurifies the exhaust gas discharged from the internal combustion engine,or at least one of an intake manifold and a cylinder of the internalcombustion engine may be set as the component that needs to be warmed.As the exhaust gas purification catalyst performs its catalytic functionat a temperature equal to or higher than the catalytic activationtemperature, it has to be heated to reach the catalytic activationtemperature and higher as quickly as possible. As the intake manifold orthe cylinders have been in cold states upon cold start-up, they have tobe warmed up as quickly as possible. The high temperature CO₂ may besupplied to the aforementioned components so as to be quickly warmed up.This makes it possible to restrain deterioration in the exhaust emissionor to improve startability of the internal combustion engine.

In the warm-up method, the temperature of the CO₂ absorbing andreleasing agent may be increased to be brought into the firsttemperature range after a command for stopping the internal combustionengine is issued, and the temperature of the CO₂ absorbing and releasingagent may further be increased to be brought into the second temperaturerange after a command for starting the internal combustion engine isissued. As the CO₂ may be absorbed by the CO₂ absorbing and releasingagent at the aforementioned timing, it may be reliably supplied to thecomponents that have to be warmed-up upon next start-up. The CO₂ isreleased from the CO₂ absorbing and releasing agent after a command forstarting the engine is issued. This makes it possible to improvestartability of the engine by warming up the intake manifold, thecombustion chamber and the like. The timing for increasing thetemperature of the CO₂ absorbing and releasing agent to reach the secondtemperature range is not limited to the one as described above. If thetemperature of the exhaust gas discharged from the internal combustionengine is low, for example, in the idling state continued for a longtime, the temperature of the exhaust gas purification catalyst may bedecreased to be below the catalytic activation temperature. It ispossible to increase the temperature of the CO₂ absorbing and releasingagent to reach the second temperature range at the aforementioned timingso as to warm up the exhaust catalyst.

A warm-up system for an internal combustion engine is provided with aCO₂ absorbing and releasing agent so as to be able to absorb CO₂contained in an exhaust gas in a first temperature range, and to releasethe CO₂ absorbed therein in a second temperature range that is higherthan the first temperature range, the CO₂ absorbing and releasing agentbeing provided to supply the CO₂ released therefrom to a component ofthe internal combustion engine. The warm-up system is provided with aheating unit that increases a temperature of the CO₂ absorbing andreleasing agent, and a temperature control unit that controls anoperation of the heating unit such that the temperature of the CO₂absorbing and releasing agent is increased to be brought into the secondtemperature range.

In the above-described warm-up system for the internal combustionengine, the CO₂ absorbing and releasing agent is provided so as to beable to supply CO₂ to components of the internal combustion engine, andthe heating unit increases the temperature of the CO₂ absorbing andreleasing agent to reach the second temperature range. Supply of the CO₂to the components of the internal combustion engine may allow theinternal combustion engine to be warmed up as quickly as possible.

The warm-up system may employ an electric heater as the heating unit.The warm-up system according to the invention may be formed into acompact body by providing the electric heater within the CO₂ absorbingand releasing agent.

The warm-up system is provided with an EGR passage that connects anexhaust passage and an intake passage of the internal combustion engine,and an EGR valve that selects an operation between connection anddisconnection of the EGR passage. In the warm-up system, the CO₂absorbing and releasing agent is provided in the exhaust passageupstream of a joint portion between the EGR passage and the exhaustpassage, an exhaust gas purification catalyst as the component thatneeds to be warmed is provided downstream of the joint portion, and thetemperature control unit controls an operation of the EGR valve suchthat the EGR passage is disconnected when the temperature of the CO₂absorbing and releasing agent is increased to be brought into the secondtemperature range. The EGR passage is blocked as aforementioned so as toprevent the CO₂ released from the CO₂ absorbing and releasing agent fromflowing into the intake passage. This makes it possible to increase thequantity of CO₂ supplied to the exhaust gas purification catalyst,promoting the warm-up of the exhaust gas purification catalyst.

The warm-up system is provided with a turbo charger having a variablenozzle in an exhaust turbine. In the warm-up system, the CO₂ absorbingand releasing agent is provided in the exhaust passage upstream of theturbo charger, an exhaust gas purification catalyst as the componentthat needs to be warmed is provided downstream of the turbo charger, andthe temperature control unit may open the variable nozzle when thetemperature of the CO₂ absorbing and releasing agent is increased to bebrought into the second temperature range. Opening of the nozzle mayreduce the pressure loss between the CO₂ absorbing and releasing agentand the exhaust gas purification catalyst. Accordingly amount of CO₂ tobe supplied to the exhaust gas purification catalyst is increased topromote the warm-up of the exhaust gas purification catalyst.

The warm-up system is provided with a turbo charger having a variablenozzle in an exhaust turbine. In the warm-up system, the CO₂ absorbingand releasing agent is provided in the exhaust passage downstream of theturbo charger, an exhaust gas purification catalyst as the componentthat needs to be warmed is provided downstream of the turbo charger, andthe temperature control unit may close the variable nozzle when thetemperature of the CO₂ absorbing and releasing agent is increased to bebrought into the second temperature range. In the case where the CO₂absorbing and releasing agent is provided downstream of the turbocharger, the nozzle is closed to prevent the released CO₂ from flowingto the upstream of the turbo charger. This makes it possible to increasethe amount of the released CO₂ to be supplied to the exhaust gaspurification catalyst downstream of the turbo charger, thus promotingthe warm-up of the exhaust gas purification catalyst.

The warm-up system is provided with an EGR passage that connects anexhaust passage and an intake passage of the internal combustion engineand an EGR valve that selects an operation between connection anddisconnection of the EGR passage. In the warm-up system, the CO₂absorbing and releasing agent is provided in the exhaust passageupstream of a joint portion between the EGR passage and the exhaustpassage, at least one of an intake manifold and a cylinder of theinternal combustion engine is employed is employed as the component thatneeds to be warmed, and the temperature control unit may control anoperation of the EGR valve such that the EGR passage is connected whenthe temperature of the CO₂ absorbing and releasing agent is increased tobe brought into the second temperature range. The EGR passage isconnected to admit the released CO₂ into the intake passage via the EGRpassage. Accordingly the CO₂ may be supplied from the EGR passage intothe intake manifold or the cylinders so as to promote the warm-up.

The warm-up system is provided with a turbo charger having a variablenozzle in an exhaust turbine. In the warm-up system, the temperaturecontrol unit may close the variable nozzle when the temperature of theCO₂ absorbing and releasing agent is increased to be brought into thesecond temperature range. The flow of the CO₂ into the exhaust passagedownstream of the turbo charger may be prevented by closing the nozzleas aforementioned. Accordingly more amount of CO₂ is admitted into theintake passage via the EGR passage, promoting the warm-up of the intakemanifold or the cylinders.

In the warm-up system, the internal combustion engine is provided with athrottle valve. According to the invention, the temperature control unitmay close the throttle valve when the temperature of the CO₂ absorbingand releasing agent is increased to be brought into the secondtemperature range. The outer air at the temperature lower than that ofthe released CO₂ may flow through the throttle valve that has beenopened, thus interrupting the warm-up function of CO₂. The throttlevalve is closed to prevent introduction of the outer air.

In the warm-up system, the temperature control unit may control theheating unit to increase the temperature of the CO₂ absorbing andreleasing agent to be brought into the first temperature range after acommand for stopping the internal combustion engine is issued, and tofurther increase the temperature of the CO₂ absorbing and releasingagent to be brought into the second temperature range after a commandfor starting the internal combustion engine is issued. The startabilityof the internal combustion engine may be improved through supply of CO₂to the intake manifold or the cylinders upon start-up of the internalcombustion engine by adjusting the temperature of the CO₂ absorbing andreleasing agent. The deterioration in the exhaust emission may berestrained by quickly warming the exhaust gas purification catalyst toreach the catalytic activation temperature and higher.

As described above, the invention may improve startability in theinternal combustion engine by supplying the high temperature CO₂released from the CO₂ absorbing and releasing agent into the intakemanifold or the cylinders. As the CO₂ is supplied to the exhaust gaspurification catalyst to quickly warm the catalyst to reach thecatalytic activation temperature and higher, the deterioration in theexhaust emission may be restrained.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of theinvention will become apparent from the following description ofpreferred embodiments with reference to the accompanying drawings,wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a schematic view of an example of an internal combustionengine in which the warm-up system of the invention is employed;

FIG. 2 is an enlarged view of a CO₂ absorbing and releasing agent shownin FIG. 1;

FIG. 3 is a flow chart of a control routine for heating an intakemanifold to be warmed up;

FIG. 4 is a flow chart of a control routine of a heater for heating anexhaust gas purification catalyst to warm up the exhaust gaspurification catalyst;

FIG. 5 is a flow chart of a control routine of a heater for heating aCO₂ absorbing and releasing agent that is allowed to absorb CO₂;

FIG. 6 is a routine of calculating a total amount of CO₂ absorbed in theCO₂ absorbing and releasing agent;

FIG. 7 is another embodiment of the internal combustion engine in whichthe warm-up system of the invention is employed; and

FIG. 8 is a flow chart showing a control routine of a heater for heatingan exhaust gas purification catalyst to be warmed up, which is executedby the ECU shown in FIG. 7.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an example of the internal combustion engine in which thewarm-up system according to the invention is employed. An internalcombustion engine 1 includes a plurality of cylinders 2, an intakepassage 3 that introduces intake air to combustion chambers 2 a formedin the respective cylinders 2, an exhaust passage 4 through which theexhaust gas flows from the combustion chamber 2 a to a point where theexhaust gas is discharged, and an intake valve 5 and an exhaust valve 6which are operated to connect or disconnect those passages 3, 4 withrespect to the combustion chamber 2 a. The intake passage 3 is providedwith a compressor 7 a of a turbo charger 7, an intercooler 8 for coolinga newly introduced air, and a throttle valve 9 for adjusting intake airquantity. The exhaust passage 4 is provided with an exhaust turbine 7 bof the turbo charger 7, and a variable nozzle 7 c that changes the flowspeed of the exhaust gas flowing into the exhaust turbine 7 b. Theopening degree of the variable nozzle 7 c is adjusted by a DC motor 11.The exhaust passage 4 is connected to the intake passage 3 through anEGR passage 14 via an EGR cooler 12 and an EGR valve 13 for circulatinga part of the exhaust gas into the intake passage 3.

The exhaust passage 4 is provided with a CO₂ absorbing and releasingagent 15 that is allowed to absorb CO₂ contained in the exhaust gas.FIG. 2 is an enlarged view of the CO₂ absorbing and releasing agent 15.As shown in FIG. 2, for example, the CO₂ absorbing and releasing agent15 has a tubular shape with one plugged end, and an electric heater 16disposed therein. The configuration of the CO₂ absorbing and releasingagent 15 is not limited to the tubular shape so long as it is capable ofabsorbing CO₂ contained in the exhaust gas and being heated to increaseits temperature by the electric heater 16. An on/off state of theelectric heater 16 may be selected by operating a switch 17. A knownproduct may be employed as the electric heater 16, for example, mainlyformed of a composite oxides of lithium such as lithium zirconate(Li₂ZrO₃), which functions in absorbing CO₂ in a first temperaturerange, for example, between 400° C. and 580° C., and releasing the CO₂in a second temperature range, for example, between 630° C. and 700° C.Hereinafter, the first temperature range and the second temperaturerange will be occasionally referred as an absorption temperature rangeand a release temperature range, respectively.

Operations of the switch 17 of the electric heater 16 is controlled byan engine control unit (ECU) 18 formed as a known computer that controlsoperation states of the internal combustion engine 1. The ECU 18performs a temperature control by executing control routines shown inthe flowcharts of FIGS. 3 to 5. The ECU 18 also controls operations ofthe throttle valve 9 or the DC motor 11 so as to adjust the intake airquantity in the internal combustion engine 1, or controls operations ofthe EGR valve 13 so as to adjust the quantity of the exhaust gas to becirculated into the intake passage 3. As the specific control methods asdescribed above are well known, detailed explanations will be omitted.

The ECU 18 executes the control routine as shown in the flowchart ofFIG. 3 such that the CO₂ absorbing and releasing agent 15 releases CO₂for warming an intake manifold 3 a in the intake passage 3 and thecylinders 2. The control routine shown in FIG. 3 is started immediatelyafter activation of the ECU 18, and repeatedly executed at apredetermined interval during the operation of the internal combustionengine 1.

In the control routine as shown in the flowchart of FIG. 3, it isdetermined whether a start-up of the internal combustion engine 1 hasbeen commanded in step S11. The determination is made based on, forexample, an operation state of an ignition switch. If it is determinedthat the operation state of the ignition switch is brought into an onstate, it is determined that the start-up of the internal combustionengine 1 has been commanded. If it is determined that the start-up ofthe internal combustion engine 1 has not been commanded, the controlroutine at the present cycle ends. Meanwhile if it is determined thatthe start-up of the internal combustion engine 1 has been commanded, theprocess proceeds to step S12. In step S12, it is determined by the ECU18 whether heating of the intake manifold 3 a is prioritized. Suchdetermination is made based on, for example, outside air temperatureupon start-up of the internal combustion engine 1. If it is determinedthat the startability of the internal combustion engine 1 isdeteriorated due to low outside air temperature, the determination ismade to prioritize heating of the intake manifold 3 a. If it isdetermined that the heating of the intake manifold 3 a does not have tobe prioritized, the control routine at the present cycle ends.Meanwhile, if it is determined that the heating of the intake manifold 3a has to be prioritized, the process proceeds to step S13. In step S13,the DC motor 11 is activated by the ECU 18 so as to fully close thevariable nozzle 7 c and to fully open both the EGR valve 13 and thethrottle valve 9.

Then in step S14, the switch 17 is brought into an on state by the ECU18 so as to activate the heater 16 for increasing the temperature of theCO₂ absorbing and releasing agent 15. In step S15, it is determined bythe ECU 18 whether the heater stop condition has been established. Theestablishment of the heater stop condition may be determined when thetime for heating the CO₂ absorbing and releasing agent 15 by the heater16 passes a predetermined time. The predetermined time is set to thevalue derived from dividing the upper limit of the amount of CO₂ thatcan be absorbed by the CO₂ absorbing and releasing agent 15 by the speedof releasing CO₂ from the CO₂ absorbing and releasing agent 15. Thepredetermined time may be set to the value as the upper limit of timefor which the temperature of the CO₂ absorbing and releasing agent 15 ismaintained in the second temperature range. The aforementioned settingof the predetermined time makes it possible to prevent unnecessaryheating of the CO₂ absorbing and releasing agent 15. The establishmentof the heater stop condition may be determined when it is determinedthat start-up of the internal combustion engine is performed. If CO₂ asinert gas is continuously supplied to the intake passage 3 even afterstart-up of the internal combustion engine 1, the combustion therein maybe deteriorated. Accordingly the heater 16 is stopped after start-up ofthe internal combustion engine 1 so as to restrain the combustiondeterioration. If it is determined that the heater stop condition hasnot been established, the control routine at the present cycle ends. Ifit is determined that the heater stop condition has been established,the process proceeds to step S16 where the switch 17 is brought into anoff state to stop the heater 16. Then the control routine ends.

Execution of the control routine as shown in FIG. 3 may introduce thehigh temperature CO₂ released from the CO₂ absorbing and releasing agent15 into the intake manifold 3 a for promoting warm-up of the intakemanifold 3 a and the cylinders 2. In the control routine of FIG. 3, theorder for executing steps S13 and S14 may be inversed.

The ECU 18 executes the control routine as shown in the flowchart ofFIG. 4 for releasing CO₂ from the CO₂ absorbing and releasing agent 15and warm an exhaust gas purification catalyst 10. The control routineshown in FIG. 4 is started immediately after activation of the ECU 18,and repeatedly executed at a predetermined interval during the operationof the internal combustion engine 1. Steps in the flowchart of FIG. 4that are the same as those in the flowchart of FIG. 3 are designated asthe same reference numerals, and the explanation thereof, thus, will beomitted.

Referring to the control routine in FIG. 4, it is determined whether astart-up of the internal combustion engine 1 has been commanded in stepS11. If it is determined that the start-up of the internal combustionengine 1 has not been commanded, the control routine at the presentcycle ends. Meanwhile if it is determined that the start-up of theinternal combustion engine 1 has been commanded, the process proceeds tostep S21. In step S21, it is determined by the ECU 18 whether thetemperature of the catalyst 10 is equal to or lower than the catalyticactivation temperature. The temperature of the exhaust gas purificationcatalyst 10 may be detected by a temperature sensor provided in thecatalyst 10 or obtained by estimating the exhaust gas temperature basedon the quantity of the fuel supplied to the internal combustion engine1. If it is determined that the temperature of the catalyst 10 is higherthan the catalytic activation temperature, the control routine at thepresent cycle ends. Meanwhile if it is determined that the temperatureof the catalyst 10 is equal to or lower than the catalytic activationtemperature, the process proceeds to step S22. In step S22, the variablenozzle 7 c is fully opened and the throttle valve 9 is fully closed bythe ECU 18. Thereafter the same steps as those shown in FIG. 3 areexecuted, and the control routine at the present cycle ends.

Execution of the control routine shown in FIG. 4 introduces CO₂ releasedfrom the CO₂ absorbing and releasing agent 15 into the exhaust gaspurification catalyst 10 for promoting the warm-up thereof, that is,heating of the exhaust gas purification catalyst 10 to reach thetemperature equal to or higher than the catalytic activationtemperature. In the control routine of FIG. 4, the order for executingsteps S22 and S14 may be inversed.

The control routine shown in FIG. 3 and the control routine shown inFIG. 4 may be independently executed or combined together. In the casewhere those control routines are combined, the respective controlroutines may be executed based on the prioritized order, or executed inparallel. The exhaust gas purification catalyst 10 may be heated toreach the temperature equal to or higher than the catalytic activationtemperature before the internal combustion engine 1 is brought into anoperation state. When improvement of the startability of the internalcombustion engine 1 is prioritized, the control routine shown in FIG. 3may be executed prior to the control routine shown in FIG. 4.

The ECU 18 executes a control routine shown in the flowchart of FIG. 5such that the CO₂ absorbing and releasing agent 15 absorbs CO₂ for thepurpose of releasing sufficient amount of CO₂. The control routine shownin FIG. 5 may be executed upon a command for stopping the internalcombustion engine 1, for example, operation of the ignition switch intothe off state, and repeatedly executed at a predetermined interval.

In the control routine shown in FIG. 5, in step S31, it is determined bythe ECU 18 whether a rate of the total amount of CO₂ absorbed in the CO₂absorbing and releasing agent with respect to the upper limit value ofthe amount of CO₂ absorbed in the CO₂ absorbing and releasing agent 15is equal to or lower than a standard rate F %. The standard rate F % isset to the value indicating the rate of the amount of CO₂ sufficient towarm the intake manifold 3 a or the exhaust gas purification catalyst 10with respect to the upper limit value of the amount of the CO₂ that canbe absorbed in the CO₂ absorbing and releasing agent 15. The totalamount of absorbed CO₂ is calculated by the routine shown in theflowchart of FIG. 6 to be described later. If it is determined that theamount of CO₂ absorbed in the CO₂ absorbing and releasing agent 15 isequal to or lower than the standard rate F %, the process proceeds tostep S32. In step S32, it is determined by the ECU 18 whether thetemperature of the CO₂ absorbing and releasing agent 15 is equal to orlower than a lower limit of the absorption temperature range. Thetemperature of the CO₂ absorbing and releasing agent 15 may be detectedby a temperature sensor provided for the CO₂ absorbing and releasingagent 15, or obtained in reference to the exhaust gas temperatureestimated based on the quantity of fuel supplied to the internalcombustion engine 1. If it is determined that the temperature of the CO₂absorbing and releasing agent 15 is equal to or lower than the lowerlimit of the absorption temperature range, the process proceeds to stepS33 where the switch 17 is operated to an on state for activating theheater 16 by the ECU 18 so as to heat the CO₂ absorbing and releasingagent 15 to reach the absorption temperature range. The control routinethen ends. If it is determined that the amount of CO₂ absorbed in theCO₂ absorbing and releasing agent 15 is not equal to or lower than thestandard rate F % in step S31, and the temperature of the CO₂ absorbingand releasing agent 15 is not equal to or lower than the lower limit ofthe absorption temperature range, the process proceeds to step S34. InS34, the heater 16 is stopped by the ECU 18, and the control routineends.

Execution of the control routine shown in FIG. 5 allows the CO₂absorbing and releasing agent 15 to absorb sufficient amount of CO₂ tobe released upon subsequent start-up of the internal combustion engine1. The ECU 18 is structured to execute the control for continuouslyoperating the internal combustion engine 1 until the CO₂ absorbing andreleasing agent 15 absorbs CO₂ by amount sufficient for the subsequentstart-up of the internal combustion engine 1, that is, the control forextending the time for stopping the internal combustion engine 1. Thismay allow the CO₂ absorbing and releasing agent 15 to absorb sufficientamount of CO₂. The CO₂ absorption efficiency of the CO₂ absorbing andreleasing agent 15 is improved especially when the CO₂ concentration ofthe exhaust gas is high and the exhaust gas quantity is small.Accordingly, the heater 16 may be activated to allow the CO₂ absorbingand releasing agent 15 to absorb CO₂ during the operation of theinternal combustion engine 1 at a high load and a low speed such thatthe exhaust gas is brought into the aforementioned state. The CO₂absorbing and releasing agent 15 is then allowed to absorb CO₂ by largeramount with the same consumption energy compared with the otheroperation state of the internal combustion engine 1. The amount of CO₂to be absorbed by the CO₂ absorbing and releasing agent 15 is reducedafter the command for stopping the internal combustion engine 1 isissued so as to reduce the energy consumed by the heater 16.

A flowchart shown in FIG. 6 represents a routine for calculating a totalamount of CO₂ absorbed in the CO₂ absorbing and releasing agent 15executed by the ECU 18. The routine shown in FIG. 6 is repeatedlyexecuted during the operation of the internal combustion engine 1 at apredetermined interval.

In the routine shown in FIG. 6, it is determined by the ECU 18 whetherthe temperature of the CO₂ absorbing and releasing agent 15 is in theabsorption temperature range in step S41. If it is determined that thetemperature of the CO₂ absorbing and releasing agent 15 is in theabsorption temperature range, the process proceeds to step S42 where anamount of CO₂ absorbed in the CO₂ absorbing and releasing agent 15,ΔCO₂add, is calculated by the ECU 18. The value of the ΔCO₂add isobtained based on parameters such as the CO₂ concentration and the flowrate of the exhaust gas as it varies depending thereon. In step S43, theECU 18 adds the value of ΔCO₂add to the total amount of absorbed CO₂,that is, CO₂strg_(i-1) that has been calculated in the previous cycle ofthe routine shown in FIG. 6 to obtain a total amount of absorbed CO₂,that is, CO₂strg_(i). The control routine at the present cycle ends.

If it is determined that the temperature of the CO₂ absorbing andreleasing agent 15 is not in the absorption temperature range, theprocess proceeds to step S44 where it is determined by the ECU 18whether the temperature of the CO₂ absorbing and releasing agent 15 isin the release temperature range. If it is determined that thetemperature of the CO₂ absorbing and releasing agent 15 is in therelease temperature range, the process proceeds to step S45 where theECU 18 calculates an amount of CO₂ released from the CO₂ absorbing andreleasing agent 15, that is, ΔCO₂sub. The value of ΔCO₂sub is calculatedbased on parameters such as the CO₂ concentration and the flow rate ofthe exhaust gas as it varies depending thereon. In step S46, the ECU 18subtracts the value of ΔCO₂sub from the value CO₂strg_(i-1) that hasbeen calculated in the previous cycle of the routine shown in FIG. 6 toobtain the total amount of absorbed CO₂, that is, CO₂strg_(i). Thecontrol routine at the present cycle then ends.

If it is determined that the temperature of the CO₂ absorbing andreleasing agent 15 is not in the release temperature range, the processproceeds to step S47 where the ECU 18 substitutes the value ofCO₂strg_(i-1) that has been calculated in the previous cycle of theroutine shown in FIG. 6 for the value CO₂strg_(i). The control routineat the present cycle ends.

The routine shown in FIG. 6 is executed to calculate the total amount ofthe absorbed CO₂ by adding or subtracting the amount of CO₂ absorbed inor released from the CO₂ absorbing and releasing agent 15. Thecalculated value of the total amount of absorbed CO₂ is stored in a RAMof the ECU 18 so as to be referenced upon execution of the subsequentcycle of the routine shown in FIG. 6 or the control routine shown inFIG. 5.

FIG. 7 shows another type of the internal combustion engine 1 in which awarm-up system according to the invention is employed. The elementsshown in FIG. 7 that are the same as those shown in FIG. 1 aredesignated as the same reference numerals. The internal combustionengine 1 shown in FIG. 7 is substantially the same as that shown in FIG.1 except that the CO₂ absorbing and releasing agent 15 is provideddownstream of the turbine 7 b and upstream of the exhaust gaspurification catalyst 10. In the case where the CO₂ absorbing andreleasing agent 15 is placed as aforementioned, the warm-up of theexhaust gas purification catalyst 10 may be promoted by the ECU 18 thatexecutes the control routine shown in the flowchart of FIG. 8. Thecontrol routine shown in FIG. 8 is started immediately after activationof the ECU 18 and is repeatedly executed at a predetermined interval.Steps in FIG. 8 that are the same as those in FIG. 4 are designated asthe same reference numerals and explanations thereof, thus, will beomitted.

In the control routine shown in FIG. 8, the process is the same as thatshown in FIG. 4 until step S21. If it is determined that the temperatureof the exhaust gas purification catalyst 10 is equal to or lower thanthe catalytic activation temperature, the process proceeds to step S51where the variable nozzle 7 c is fully closed by the ECU 18. The processis executed in the same manner as in the control routine shown in FIG.4, and the control routine at the present cycle ends.

In the case where the CO₂ absorbing and releasing agent 15 is placed ata position as shown in FIG. 7, the variable nozzle 7 c is fully closedto block the flow of the CO₂ to the upstream of the turbine 7. Theamount of CO₂ flowing into the exhaust gas purification catalyst 10 isthen increased to promote the warm-up of the exhaust gas purificationcatalyst 10. In the control routine shown in FIG. 8, the order forexecuting steps S51 and S14 may be inversed.

The invention may be structured into arbitrary forms without beinglimited to the aforementioned embodiments. The position at which the CO₂absorbing and releasing agent is placed is not limited to the exhaustpassage so long as it is able to absorb CO₂ contained in the exhaustgas. The CO₂ absorbing and releasing agent may be placed in the EGRpassage. The number of the CO₂ absorbing and releasing agents to be usedand positions thereof may be arbitrarily determined. A plurality of CO₂absorbing and releasing agents may be provided around a plurality ofcomponents that need to be warmed such that high temperature CO₂ can besupplied directly to those components. The heating unit is not limitedto the electric heater. A combustion type heater may be employed forheating the CO₂ absorbing and releasing agent.

The components in the internal combustion engine, which need to bewarmed are not limited to the exhaust gas purification catalyst, intakemanifold, and cylinders. A lubricating oil tank may be provided suchthat heat exchange can be performed between the released CO₂ and thelubricating oil for smoothly increasing the temperature of thelubricating oil upon start-up of the internal combustion engine in orderto prevent deterioration in the startability thereof caused by highviscosity of the lubricating oil. The warm-up of the internal combustionengine may be promoted by supplying heat of CO₂ released from the CO₂absorbing and releasing agent into various components that need to bewarmed.

1-13. (canceled)
 14. A warm-up method for an internal combustion engine,comprising; increasing a temperature of the CO₂ absorbing and releasingagent, which absorbs CO₂ contained in an exhaust gas in a firsttemperature range and which releases the CO₂ absorbed therein in asecond temperature range that is higher than the first temperaturerange, to the second temperature range which is higher than the firsttemperature range; and supplying the CO₂ released from the CO₂ absorbingand releasing agent into a component of the internal combustion engine.15. The warm-up method according to claim 14, wherein the componentcomprises an exhaust gas purification catalyst that purifies the exhaustgas discharged from the internal combustion engine.
 16. The warm-upmethod according to claim 14, wherein the component comprises at leastone of an intake manifold and a cylinder of the internal combustionengine.
 17. The warm-up method according to claim 15, wherein thecomponent comprises at least one of an intake manifold and a cylinder ofthe internal combustion engine.
 18. The warm-up method according toclaim 14, wherein the temperature of the CO₂ absorbing and releasingagent is increased to be brought into the first temperature range aftera command for stopping the internal combustion engine is issued, and thetemperature of the CO₂ absorbing and releasing agent is furtherincreased to be brought into the second temperature range after acommand for starting the internal combustion engine is issued.
 19. Thewarm-up method according to claim 15, wherein the temperature of the CO₂absorbing and releasing agent is increased to be brought into the firsttemperature range after a command for stopping the internal combustionengine is issued, and the temperature of the CO₂ absorbing and releasingagent is further increased to be brought into the second temperaturerange after a command for starting the internal combustion engine isissued.
 20. The warm-up method according to claim 16, wherein thetemperature of the CO₂ absorbing and releasing agent is increased to bebrought into the first temperature range after a command for stoppingthe internal combustion engine is issued, and the temperature of the CO₂absorbing and releasing agent is further increased to be brought intothe second temperature range after a command for starting the internalcombustion engine is issued.
 21. The warm-up method according to claim17, wherein the temperature of the CO₂ absorbing and releasing agent isincreased to be brought into the first temperature range after a commandfor stopping the internal combustion engine is issued, and thetemperature of the CO₂ absorbing and releasing agent is furtherincreased to be brought into the second temperature range after acommand for starting the internal combustion engine is issued.
 22. Awarm-up system for an internal combustion engine, comprising; a CO₂absorbing and releasing agent that absorbs CO₂ contained in an exhaustgas in a first temperature range, and releases the CO₂ absorbed thereinin a second temperature range that is higher than the first temperaturerange, a heating unit that increases a temperature of the CO₂ absorbingand releasing agent; and a temperature control unit that controls anoperation of the heating unit such that the temperature of the CO₂absorbing and releasing agent is increased to be brought into the secondtemperature range, wherein the CO₂ absorbing and releasing agent isprovided to supply the CO₂ released therefrom to a component of theinternal combustion engine.
 23. The warm-up system according to claim22, wherein the heating unit comprises an electric heater.
 24. Thewarm-up system according to claim 22, further comprising an EGR passagethat connects an exhaust passage and an intake passage of the internalcombustion engine, and an EGR valve that selects an operation betweenconnection and disconnection of the EGR passage, wherein: the CO₂absorbing and releasing agent is provided in the exhaust passageupstream of a joint portion between the EGR passage and the exhaustpassage; the component comprises an exhaust gas purification catalystprovided downstream of the joint portion; and the temperature controlunit controls an operation of the EGR valve such that the EGR passage isdisconnected when the temperature of the CO₂ absorbing and releasingagent is increased to be brought into the second temperature range. 25.The warm-up system according to claim 22, further comprising a turbocharger having a variable nozzle in an exhaust turbine, wherein the CO₂absorbing and releasing agent is provided in the exhaust passageupstream of the turbo charger; the component comprises an exhaust gaspurification catalyst provided downstream of the turbo charger; and thetemperature control unit opens the variable nozzle when the temperatureof the CO₂ absorbing and releasing agent is increased to be brought intothe second temperature range.
 26. The warm-up system according to claim22, further comprising a turbo charger having a variable nozzle in anexhaust turbine, wherein the CO₂ absorbing and releasing agent isprovided in the exhaust passage downstream of the turbo charger; thecomponent comprises an exhaust gas purification catalyst provideddownstream of the turbo charger; and the temperature control unit closesthe variable nozzle when the temperature of the CO₂ absorbing andreleasing agent is increased to be brought into the second temperaturerange.
 27. The warm-up system according to claim 22, further comprisingan EGR passage that connects an exhaust passage and an intake passage ofthe internal combustion engine and an EGR valve that selects anoperation between connection and disconnection of the EGR passage,wherein the CO₂ absorbing and releasing agent is provided in the exhaustpassage upstream of a joint portion between the EGR passage and theexhaust passage; the component comprises at least one of an intakemanifold and a cylinder of the internal combustion engine; and thetemperature control unit controls an operation of the EGR valve suchthat the EGR passage is connected when the temperature of the CO₂absorbing and releasing agent is increased to be brought into the secondtemperature range.
 28. The warm-up system according to claim 27, furthercomprising a turbo charger having a variable nozzle in an exhaustturbine, wherein the temperature control unit closes the variable nozzlewhen the temperature of the CO₂ absorbing and releasing agent isincreased to be brought into the second temperature range.
 29. Thewarm-up system according to claim 22, wherein: the internal combustionengine is provided with a throttle valve; and the temperature controlunit closes the throttle valve when the temperature of the CO₂ absorbingand releasing agent is increased to be brought into the secondtemperature range.
 30. The warm-up system according to claim 22, whereinthe temperature control unit controls the heating unit to increase thetemperature of the CO₂ absorbing and releasing agent to be brought intothe first temperature range after a command for stopping the internalcombustion engine is issued, and to further increase the temperature ofthe CO₂ absorbing and releasing agent to be brought into the secondtemperature range after a command for starting the internal combustionengine is issued.